SDTM Timing Variables for Pre-study Findings

Data about medical history and prior meds are often collected at an initial study visit. Records in an SDTM-based dataset for these events and interventions will include information about their starts and ends, either in dates or relative timing variables, and will usually also include --DTC, the date when the data were collected, and visit variables (VISITNUM, VISIT, VISITDY), which represent the visit when the data were collected. The value in --DTC is the date of the visit, or for multi-day visits, a date within the date range of the visit.

That initial visit may also include collection of pre-study findings data, such as a test performed at the time the disease under study was diagnosed, or a pre-existing test result used to establish eligibility. In such a case, the visit variables will represent the visit when the test result was recorded in the CRF. However, --DTC is the date of the test (or sample collection), not the date when the finding was recorded, so it will not be the date of the visit. The --DTC may occur much earlier than informed consent and the start of the study and if the date in --DTC is complete, so that --DY can be calculated, --DY may be a large negative number.

The SDTM for findings does not include a separate variable for the date when the result of a finding was collected. Usually this date is not of interest, since the results of a finding apply to the time when the test was performed, not the time when the test results were collected for the study. Although a findings record for a pre-study finding does not include the date when the data were collected for the study, the inclusion of the visit variables is generally sufficient to indicate when the data were collected.